Title:
Equipment for on-site repair of a composite structure with a damaged zone and corresponding method
United States Patent 6206067
Abstract:
The present invention relates to on-site repairs of a composite structure (10) such as an aircraft structure in which a concave recess (14) is machined in the damaged zone, a non-polymerized composite part (16) is set into said recess and part (16) is polymerized under pressure using tooling (18) comprising a stack of plates (32) that increase the pressure applied to the composite part. The present invention thus obtains invisible repairs with mechanical characteristics that are similar to those of the initial structure.


Inventors:
Kociemba, Fabienne (Toulouse, FR)
Soro, Daniel (Jouy/Seine, FR)
Application Number:
09/423208
Publication Date:
03/27/2001
Filing Date:
01/20/2000
Assignee:
Aerospatiale Societe Nationale Industrielle (Paris, FR)
Primary Class:
Other Classes:
156/71, 156/94, 156/98, 156/285
International Classes:
B29C43/36; B29C73/10; B29C73/32; B64F5/00; (IPC1-7): B32B31/00
Field of Search:
156/71, 156/94, 156/98, 156/285, 156/382
View Patent Images:
Foreign References:
EP01808651986-05-14Blind side panel repair patch.
FR2705914A11994-12-09
Other References:
Dastin, S., "Repairing Advanced Composite Materials," Machine Design, vol. 58, No. 4, Feb. 1986, pp. 86-90.
Primary Examiner:
Sells, James
Attorney, Agent or Firm:
Burns, Doane, Swecker & Mathis, LLP
Claims:
1. 1. Tooling for on-site repairs of a composite structure, having an outersurface and a concave recess previously machined in a surface of thecomposite structure, for high pressure polymerization of a non-polymerizedcomposite part including a shape that matches that of the concave recess,the tooling comprising:PA1 a bladder including a peripheral edge capable of being fastened around thenon-polymerized composite part such that it forms a hermetic leaktightseal between the peripheral edge and the composite structure outersurface;PA1 a stack of plates including at least two plates interposed with the bladderand the non-polymerized composite part, wherein the plate proximate to thebladder has a surface area greater than a surface area of the plateproximate to the non-polymerized composite part, whereby pressure on thenon-polymerized composite part is increased;PA1 means for connecting the bladder to an external source of negativepressure; andPA1 means for heating the non-polymerized composite part.NUM 2.PAR 2. Tooling of claim 1 wherein the plate proximate to the bladder has asurface area of at least twice the surface area of the plate proximate tothe non-polymerized composite part.NUM 3.PAR 3. Tooling of claim 1 wherein the plates are preferably leaf metal platesthat can be stretched to take the shape of the composite structure.NUM 4.PAR 4. Tooling of claim 1 wherein means for guiding the plates relative to oneanother are provided.NUM 5.PAR 5. Tooling of claim 4 wherein the guiding means comprise at least oneguiding pin that projects perpendicularly out of at least one of theplates through guiding holes provided in the other plates.NUM 6.PAR 6. Tooling of claim 1 wherein the plate that is closest to composite parthas a surface and a shape that are more or less identical to those of saidcomposite part at the surface of the composite structure.NUM 7.PAR 7. Tooling of claim 1 wherein the heating means comprise a heating capinterposed between the bladder and the stack of plates.

Description:

PAC BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, as anon-limitative example, in reference to the attached drawing in which thesole FIGURE is a schematic representation, shown in a partial crosssection, of on-site repair tooling according to the invention positionedon a composite structure with a damaged zone. PAC DETAILED DISCLOSURE OF A PREFERRED EMBODIMENT OF THE INVENTION

In the sole FIGURE, reference number 10 is a general reference to acomposite structure, such as an aircraft structure. The outer surface 12of the composite structure 10 has a concave recess 14 that has beenpreviously machined using known tooling not included in the invention.

Recess 14 has been machined in a damaged zone of composite structure 10which is to be repaired on site. The recess 14 has an overall circularshape when seen from above but it may, however, have a different shape,such as an oval, depending on the shape of the damaged zone.

In addition, recess 14 is either step machined, as seen in the FIGURE, orscarf machined using known techniques. Recess 14 is preferably scarfmachined as this enables mechanical characteristics to be obtained in thedamaged zone that are greater than those obtained when the recess is stepmachined.

Once recess 14 has been machined a composite part 16 is set into therecess, the shape of said composite part matching that of the recess. Itshould be pointed out that "composite part" does not refer to apre-polymerized part but to a non-polymerized assembly comprising longfibers, for example carbon fibers, and an adhesive, such as an epoxy resinto which a softener has been added. Consequently, composite part 16 may bemade directly on-site without it being necessary to use an autoclave.

In practice, and using known techniques, composite part 16 can be madeeither by cutting and superimposing layers of fabric that have beenpre-impregnated with resin or by cutting and superimposing layers of dryfabric, being careful to impregnate them layer by layer as they are set inplace. Another alternative is to cut and superimpose alternate layers ofdry fabric and solid films of adhesive. This technique is preferred as itis easy to perform and obtains high quality results.

According to the invention, composite part 16 is set into recess 14 andpolymerized under pressure on the site where composite structure 10 islocated. Said composite part is polymerized using repair tooling given theoverall number 18.

Repair tooling 18 mainly comprises a leaktight bladder 20, means 22 forheating composite part 16 and means 24 for increasing the pressure appliedto said composite part.

The leaktight bladder 20 is slightly larger than composite part 16, suchthat the peripheral edge may be pressed to form a leaktight seal againstouter surface 12 of composite structure 10 around composite part 16 usinga leaktight putty 26.

The leaktight bladder 20 is equipped with a valve 28 that constitutes meansfor connecting the bladder to an external source of negative pressure (notshown). No further description of this arrangement will be given as it isstandard technology.

In this example, means 22 for heating composite part 16 comprise a heatingcap that is connected to an external power supply (not shown) byelectrical conductors (not shown). The heating cap that constitutes themeans 22 for heating composite part 16 is interposed between bladder 20and pressure increasing means 24.

Pressure increasing means 24 constitute the essential characteristic of theinvention. They are interposed between bladder 20 and composite part 16,such that the load applied to said composite part is increased when thespace 30, formed by composite structure 10 and leaktight bladder 20, isput under negative pressure.

In the preferred embodiment of the invention shown in the sole FIGURE,pressure increasing means 24 comprise a stack of plates 32 whose surfacesgradually increase towards bladder 20. More precisely, the surface and theshape of the plate 32 that is closest to composite part 16 are more orless identical to those of said composite part 16 on the outer surface 12of composite structure 10. In practice, the plate 32 that is closest topart 16 generally has a slightly larger surface area than that of thesurface 12 of part 16.

Moreover, the plate 32 that is closest to composite part 16 is centered onsaid composite part such that it totally covers the part.

In addition, the plate 32 that is closest to bladder 20 has a surface thatis, for example, at least twice that of the plate 32 that is closest tocomposite part 16. Consequently, when a vacuum is created in space 30 thepressure applied to composite part 16 by the plate 32 that is closest tosaid part is more or less twice the pressure applied by leaktight bladder20 to the plate 32 that is furthest away from the composite part.

Given that the degree of negative pressure created in space 30 is generallybetween 0.7 and 0.9 bar for the primary vacuum sources that are most oftenused in this application, the addition of pressure increasing means 24enable at least twice the pressure to be applied compared to that appliedwith standard tooling. Thus, and purely as an example, pressure measuringapproximately 3 bar can be applied to composite part 16 with a 0.9 barvacuum in space 30 and a 3.75 surface ratio.

It should be noted that the pressure increase factor depends on the ratioof surfaces between the most distant plates of the stack of plates 32,such that the ratio may vary by a factor of three and still remain withinthe scope of the present invention.

The number of plates 32 constituting the stack can be equal to two andthese plates can be rigid when outer surface 12 of composite structure 10is plane or has a continuous curve of a known value.

In the example of tooling intended to repair the composite structures ofaircraft the outer surface of these structures is not generally planar andmay have varying degrees of curvature. In this event pressure increasingmeans 24 are preferably used in which the plates 32 are constituted by arelatively large number of leaf metal plates that can be stretched to takethe shape of surface 12 of the composite structure to be repaired.

Relative guiding means are preferably provided to prevent plates 32 slidingagainst each other when space 30 is put under negative pressure.

In the embodiment shown in the sole FIGURE these relative guiding meanscomprise a guiding pin 34 that projects perpendicularly out of at leastone of the plates 32 through guiding holes 36 provided in the other plates32. In the example shown, guiding pin 34 is fastened to the center of theplate 32 that is closest to bladder 20 and guiding holes 36 are providedin the center of the other plates 32. It should be noted that otherarrangements are also possible, such as several guiding pins 34 beingfastened to the same plate 32 or to different plates.

The length of the guiding pin(s) 34 is designed to enable the remainingplates 32 to be guided without, however, the pin(s) projecting beyond thestack of plates. Therefore, the length of the pin(s) is slightly shorterthan the accumulated thickness of plates 32 that do not bear any pins.

In the sole FIGURE plates 32 are shown to have spaces between them. This isintended to make the drawing clearer and it is for this reason that pin 34does not pass through certain plates 32.

It should be noted that the relative guiding means of plates 32 may have adifferent shape in other modified versions.

A guiding liner 33, positioned around the stack of plates 32, preventsbladder 20 from becoming caught under the stack or between two plates whenspace 30 is put under negative pressure.

In the above-mentioned example, where only two plates 32 are used, guidingliner 33 that is interposed between composite structure 10 and the bladderaround the stack of plates can ensure the relative guiding of plates 32.

The repair tooling 18 of the invention also comprises all the componentsthat generally equip tooling of the prior art. These various componentswill now be briefly described in reference to the FIGURE.

A drainage fabric 38, the measurements of which are slightly greater thanthose of heating cap 22, is interposed between said heating cap andleaktight bladder 20. This drainage fabric 38 is used to evacuate aircompletely when space 30 is put under negative pressure.

The remaining components of repair tooling 18 are positioned betweencomposite part 16 and pressure increasing means 24. Starting fromcomposite part 16, these various components comprise a de-molding fabric40, a perforated plastic film 42, a drainage fabric 44, a leaktight film46 and a Mossite film 48.

The de-molding fabric 40 is used to separate tooling 18 from part 16 afterpolymerization.

The perforated plastic film 42 operates in conjunction with drainage fabric44 and leaktight film 46 to evacuate air and excess resin towards theperiphery when space 30 is put under negative pressure.

Finally, Mossite film 48, which is optional, ensures that the pressureapplied to composite part 16 through pressure increasing means 24 isevenly spread.

When a composite structure 10 with a damaged zone is repaired, first of alla concave recess 14 is machined in structure 10 to eliminate all thedamaged zones.

Should the damage extend through the entire thickness of compositestructure 10, recess 14 must also cross through said thickness. A thincomposite plug is then bonded to the base of the recess before thefollowing operations are carried out.

The non-polymerized composite part 16 is then set into recess 14, asdescribed above.

The repair tooling 18, described above, is then installed by connectingvalve 28 to the external source of negative pressure and by connectingheating cap 22 to the external power supply.

The adhesive contained in composite part 16 is polymerized under pressurewhen composite part 16 is heated by heating cap 22 and is put underpressure by space 30 coming under negative pressure. More precisely,pressure, for example of approximately 3 bar, is applied to composite part16 due to the amplifying action of pressure increasing means 24.

When the polymerization has finished the heating stops and space 30 isreconnected to the outside atmosphere. Repair tooling 18 can then beremoved.

Tests carried out using tooling of this kind show that the externalappearance of surface 12 is unchanged in the repaired zone and that themechanical characteristics in said zone are respectively 79% and 89% ofthose of the initial structure, depending on whether a step machined or ascarf machined recess 14 is used. The mechanical characteristics aretherefore considerably greater than those obtained using techniques of theprior art and enable repair work to be carried out on a far larger scalethan has previously been possible.